Automatic commutator



Dec. 1, 1931. G. PEDRAzzo 1,334,639.

AUTOMATIC COMMUTATOR Original Filed Aug. 21, 1929 3 Sheets-Sheet l Dec. i931. G. PEDRAz'zo y 1,834,639

Au'rolwrxc collu'rAToR Y 'Y origin-g1 Filed Aug. 21. 1929 s sheets-sheet s Patented Dec. 1, 1931 UNITED STATES GIOVANNII- PEDRAZZO, OF BIELLA, ITALY AUTOMATIG CDMMUTATQR Application led August 21, 1929, Serial machine under varying working conditions.

The device according to the invention consists substantially 1n a serles of electromagnets which are arranged radially or in a sp1- w der-like manner with suitable angular distances between adjacent ones, and these electromagnets act on a central movable core whichis keyed to the shaft of the controller. The current furnished to these electromagnets is automatically controlled by means of relays in combination with other well known devices or by means of new devices which will hereafter be described, these relays or other devices being placed under the control of the variation of the intensity of the electric current absorbed by the' machine, and the electromagnets through exerting a purely magnetic action on the core which they surround, cause the core and thus also the shaft of the vcontroller to be shifted angularly to obtain the desired automatic operation of the controller.

The core may be single or double; that is, it may be applied to one side only of the shaft or to both sides, and the number of the elec'- tromagnets may be equal to the number of the power outputs that may be obtained or be smaller than such number.` For example one electromagnet may be provided for each two power outputs, in which case the commutation is obtained, for example with a double core, by using the core on one side of the shaft for the Ilower outputs and causing the core on the other side 'to enter into action in* order to continue the rotation of the shaft of the controller for the higher outputs.

The movable single core, or the double -core ing part of the Control Shown in Fig. 7,

which is used when the number of the electromagnets is smaller than the number of the obtainable output values, ends in a cylindrical surface and covers in any one of its positions of insertion ofthe 4various powers not only the respective electromagnet, but also a small portion of the neighbouring electromagnet or electromagnets towards which No. 387,475, and 1n Italy september 4,' 192s. Renewed July 1s, 1931.

it must be shifted, for the evident purpose of increasing the rotation couple from the neighbouring electromagnets when one of them is being fed in order to change the power.

A suitable retarding device is provided to prevent the electromagnets being fed for momentary variations of the load, as they are intended to be fed only as a result of persistent variations.

The invention will be described with reference to the accompanying drawings which show by way of example several exemplications of my invention. In the drawings Fig. l is a front view of a commutating device for eight power output values Fig. 2 is a front view and Fig. 3 a sectional View of a commutating device for three output values,

Fig. 4 shows by way of example one of the arrangements that may be .adopted for the automatic control, b means of relays, of

the supply of the windings of the electro* magnets for the shifting of the controller in machines having eight output values and an equal number of electromagnets for operating the controller,

Fig. 5 is a detail View of a relay to be used in the arrangement shown in Fig. Ll, and of the respective retarding device,

Fig. 6 shows schematically in a perspective view and in a corresponding development, a cam intended to obtain mechanically an arrest which prevents the simultaneous working of several electromagnets,

Fig. 7 is a scheme of an automatically operated control device with relays for a machine capable of furnishing six output values and employing only three electromagnets,

Fig. 8 is a detail sectional View of the electromagnets, the core and the brushes form- F ig. 9 shows a 'development and a perspective View of a cam for obtaining me* chanically an arrest to prevent a simultaneousv working of severa-l electromagnets, and

Fig. 10 shows a detail of a control e`ected bymeans of brushes and intended to prevent a sudden passage from-the maximum to the minimum power, and vice versa.

As shown in Fi l to3, the shaft e of the controller hasl eyed to it a hub member f which carries a core made of laminated iron and which4 is a single core 1n Fig. land a double core` in Fig. 2. This core is .exposed to the purely'magnetic action of a l and provided with a lever having 'a roller,

and with a spring so that when one half of a revolutiqn has been completed the spring causes the segments of the controller to res,

I turn into the normal position.

i output values.

An arrangement for amachine having n output values is shown by way of example in 1 where the n electromagnets I, II, III are arranged inv a spider-like formation at equal angular distances 1.1/l apart. In another arrangement the number 'of the electromagnets may be equal to The ligure shows an arrangement for eight The movable `core g which terminates with a cylindrical surface, covers in each of the n positions the respective electromagnet' and in addition, a short length of the two 'neighbouring electromagnets. The angle between two neighbouring electromagnets may be reduced in case the number n of the outlet values is small, so that the core twill not bey excessively large, and in this case the maximum angular displacement of the shaft will be less. i

When the number n of the output values is small, the arrarigement....shown in Fig. 2 may be used (controller for three values), wherein the electromagnets are alsoW arranged -at equal angular distances apart and a doubleco're is used, the two parts of which work alternately. In this latter case the displacelment of the shaft of the controller in passing from one value'to the other is (60 in the figure). In this case the core on one side covers only one of the electromagnets and the core on the other side covers a portion of the electromagnets towards which the core is to be shifted.

The

automatic control without the insertion of a mechanical friction resistance, and thereforea reliable operation without the need of lubrication and supervision.

The following description of an automatic control device with relays as shown in Figs. 4, 5 and 6 is given only by way of example to explain the automatic working of the commutating device according to the invention, it being understood that the construction may be varied in many way within the limits of the claims. r

In the upper part of Fig. 4, the letter L and the numbers from l to 15 designate the theoretical scheme of a three-phase current machine capable of developing eight output values in accordance with the invention described in an earlier application for patent of the applicant. i

This controhdev'ice consists of a system of rela-ys which are acted on bythe vari ation' of the intensity of the' current absorbed by the various outputs. The primaries of four current reducers a, b, c, d, the secondaries of which provide current respectively to the circuits of four relays indicated IV-VIIL III-VII, II-VI and I-V, are inserted in series with four suitable circuits indicated m, m,-m, m. For low outputs the current reducers a, b, c, d may be omitted and the circuits m, m', m, m" may be made to pass directly through the said relay. The relay IwV which is'fed by the current reducer al, connects with the intermediate electromagnets II, VI and IV, the second relay II-v-VI which is fed by the current reducer c, connects with the minimum electromagnets III, I and the clectromagnet-s VII and V, the third relay which is fed by the current reducer Z), connects with the electromagnets IV, II, VIII (maximum) and VI, while the fourth relay IV-VIII which is fed by the current reducer a, connects with the electromagnets V, III and VII. y

The details of a relay are shown in Fig. 5, whichshows that the action of the intensity of the current, which acts through a current coil h on a magnetic bar i, in combination with the action of a push-pull spring y', produces the displacement of a small lever Z which by means of contact elements Z', l may establish two different contacts, an upper one `o when the current increases and a lower one p when the cur/rent diminishes. For this purpose the lever l engages with its free end a fork g carried by an extension of the magstantaneous and non-persisting variations of the load. .f

In order to.avoid a strong pull on the spindle of the relay, the current coil enclosed within the magnet may be constructed with two internal cores of thin sheets of iron of which one is stationary and is traversed by the spindle while the other one, is secured on the spindle. proaching ends, one in the shape' of a point, and the'other provided with a recess, and externally of the current coil is provided a sheath of wound sheet iron-which carries covering pieces at its two ends." In this way the relay is transformed into a magnetic compensation relay.

Fig. 4 shows the revolving commutator keyed to the shaft e of the controller. The eight electromagnets I, II, III, IV, V, VI, VII and VIII are connected on the one hand with the contacts o and y? of the relays, and on the other hand with eight metallic segments with which the central rotating core comes successively into contact. The supply to the electromagnets is obtained through the contacts of the relays from the secondary of a tension reducer t, the primary of which is inserted in shunt between two lines of the machine, or may also be connected directly, viz. without the tension reducer t, in case the tension is not very high. The feeding circuits of the electromagnet-s are shown with thin lines.

The central core of the commutator faces, in each of the eight positions, three successive segments, with the exception of the two extreme positions, in which it faces only two segments. For this purpose the iirst and the last segments are cut in such a way as to leave between them a sufficient space that when the core has arrived in one of its eXtreme positions, the core will not be attracted by the electromagnet which represents the other eX- treme position, and so that the movement of the controller will alwaystake place by steps; this also prevents a simultaneous entrance of current into two coils of the electromagnets. Moreover, in order to avoid several electromagnets entering into action simultaneously, a mechanical arresting device' iS provided, as shown in Fig. 6. The four relays IVVIII, III-VII,\ IIVI and I-V are arranged aroundthe spindle of the controller at angular distances which are means of the rheostats u, u', u, u"

equal to those of the magnetic electromagnets I, II, III, IV, V, VI, VII and VIII (450 in the figure), and the displacements of their movable spindles z' will or will not bevpossible according to the position of a cylindrical double-proled cam s which is arranged concentrically respecting the shaft e of the controller. This arrangement will be described with reference to Fig. 7.

The sensitivity of the device is adjusted by and ing controller and with four contacts .fr

These two cores have their ap-` of slides fv, o', fu, fv". The slides z, e', a, 2 together with a projection w on the rotatm" are used to short-circuit a portion o the said rheostats of the lower powers. All this will be more clearly described with reference to the scheme shown in Fig. 7.

In the upper part of Fig. 7 the letter L and the numbers from 1 to 12 indicate a theoretical scheme of a-machine working on three phase current with six outputs (machine Pedrazzo). In this case the arrangement -for the automatic control also consists in a system of relays acted on by the variation of the intensity of the current absorbed by the various outputs. The primaries of three current reducers a, b, c, are inserted in series with the three Circuits of the machine, the secondary circuits of which reducers feed respectively the circuits of three relays which are numbered III-VI, II-V and I-I V. The relay I-IV which is fed by the reducer c, connects with the electromagnets II, V and VI (intermediate) g the second relay II-V fed by the reducer b connects with the electromagncts III, VI (maximum), I (minimum) and IV; the third relay III-VI which is fed by the reducer 0;, connects with the intermediate electromagnets IV, II and V. The relays may be of the type illustrated in Fig. 5 or preferably of the type having a. magnetic compensation, as above described.

The revolving commutator shown in Fig. 7 has a double core g and is fitted for the siX outputs with but the three electromagnets I-IV, II#V, III-VI which are arranged at an angle of 60 apart. The three electromagnets are fed through the.contacts o, p of the relays from the secondary of a tension reducer t, as in Fig. 4, preferably with the addition of acondenser T which serves to reduce sparking and the like. In each of the six positions of commutation the central core g covers with one or the other of its sidesI not only the respective electromagnet, but also a portion of the electromagnet towards which it must be attracted. The commutator is shown in the drawings .by way of example in the Aposition of the III value of output and with the core 'on this side covering a portion of the central electromagnet II-V in order to be made to pass into the II position when the intensity' of the current absorbed by the machine continues to drop beneath a certain limit, and the contact p therefore is closed, while the core on the opposite side covers a portion of theelectroma-gnet I-IV so that it can go over into the IV position when the intensity of the current increases beyond a certain limit, the contact o being closed in this case. Y

In order to prevent several electromagnets working simultaneously there is also provided in this case a mechanical cam operated arresting device as shown in Fig. 9.

The cam s (Figs. 6 and 9) is provided with recesses which are diametrically opposite each other in pairs, so that only the relay corresponding to the output which is inserted (third output in the drawings) is free to work, while the other relays are held in the middle position and are thus' not working. In this way, when the current is comprised between the maximum and minimum limit corresponding to a given output (III output value inthe drawings) none of the electromagnets remains under tension, while only one electromagnet at a time may enter into action and its insertion is instantaneous. The consumption of energy in the device therefore is quite small, because it is limited to the energy absorbed by the three current-responsive circuits of the relays which are fed with a low tension. l

The sensitivity of the device is adjusted in the following mann-er. With each of the current circuits is inserted in series a rheostat u', u, u with slide fv, o, 12 for the desired regulation of the maximum and minimum value of the current which is to be assigned to each output value independently of the value assigned to the others; this is of the greatest importance, more especially when in case of a large number of power-output values the limits of intensity between the successive values are somewhat vague and in-- definite. It is further possible to 'assign a different cut-out sensitivity to the various output values even during the working of the motor. This adjustment during the working of the motor may be easily carried through, especially if during the construction due care has been taken to arrange the various rheostats in an easily accessible position.

Figs. 4 and 7 show an arrangement in which each relay is made to serve for two output values; they refer to a type of Winding in which for the first outputs (of l'ow values) the circuitsare inserted in star connection and for the last (higher) outputs, in delta connection; in this way the same relay may be used for a couple of values. correspending vto the star-delta connectlon by merely varying the current of the relays 1n a given ratio. This is obtained by short-circuiting for the first values (star connected) a portion of thegresistance or rheostat u', u, u" inserted in the circuits of the relays, by means of a projection fw placed on the revolving controller, the contacts a', and a slide a', z, 2 one of each of said elements being provided for each of the said rcsistances, which may be adjusted for a perfeet adjustment of the apparatus. The current at the projection lw is carried by means of a brush f, which slides on a conductor ring f which is mounted on an insulating supporting disc f secured to the hub f of the core so that it may rotate therewith.

In order to prevent in the arrangement shown in Fig. 7 the commutator passing suddenly from the maximum to the minimum or from the minimum to the maximum power,

viz. in order to prevent its being attracted,

so as to make a complete revolution, while it must make only five partial rotations of 6()o in one or the other direction, but never the partial rotation of 60 between the extreme powers, a device may be used such as the one shown in Fig. l0. This device consists of a ring y which too is mounted by means of an insulator on the hub f of the core, and which is conducting throughout but a portion of its length, being interrupted by an insulating piece y. The current which arrives from the reducer Z is furnished to the electromagnets III--VI and I-IV through the saidring g/ and through a brush y. The ring is shown in Fig. l0 in the position which corresponds to the commutator being in the I output value. The current coming from the reducer t is interrupted at the electromagnet III-VI -as the brush which conducts the current to this electromagnet bears on the insulatingr part of the ring y. A diminution of the intensity of current absorbed therefore has no influence on the rotating commutator. On the other hand, when the commutator is in the position corresponding to the VI output value, the insulating part y of the ring y is in the position shown in dotted lines, and

more precisely in front of another brush ym which therefore cannot carry current to the electromagnet I-IV, so that an increase of the intensity of current absorbed cannot produce a movement of the rot-ating commutator.

It is evident that when the number of the 'output values is different from the one shown and described, the number of Athe relays and of the electromagnets will also be diii'erent; the circuits however are quite similar to those shown in Fig. 4 or 7 and only the number of the various elements will be varied. It is and polyphase current electromagnets which are fed by a suitable relay-interrupter attracted by the contacts o and p of the relays shown in Figs. 4 and 7 or by any other suitable arrangement of relays. Further, the invention is not limited to the use of the automatic device for machines with several powers, but alsoy comprises the use of the device for other purposes Where it may be employed.

What I claim is: v

l. An automatic commutation device for electric machines having a plurality of output values, comprising a,series of substantially concentric electromagnets arranged in a spiderlilrc fashion at substantially equal angular distances from each other, a controller having a shaft, a movable central core on said shaft and on which the said electromagnets act, and means actuated as an incident to the variation in the intensity of the current absorbed by the machine, for selectively actuating the electromagnets, whereby the latter by their magnetic action on the core impart desired movement thereto, to produce selective 4angular displacement thereof and consequent automaticoperation of the controller.

2. An automatic commutation device for electric machines having a plurality of output values, comprising a series of substantial# ly concentric electromagnets arranged in a spider-like fashion, a controller having a shaft, a movable central core on said shaft and on which the said electromagnets act,

means actuated as an incident to the variation in the intensity of the current absorbed by the machines, for selectively actuating only one of the electromagnets at a time, whereby the latter by its magnetic action on tho core imparts desired movement thereto, to produce selective angular displacement thereof and consequent automatic operation of the controller, and means for automatically cutting of the current from the said electromagnet When the core is reaching its neXt angular position.

In testimony whereof I have signed my' name to this specification.

' GIOVANNI PEDRAZZO. 

